Introduction Mesenchymal hamartoma of the liver (MHL) is an uncommon, benign lesion occurring primarily in the pediatric population. While the exact pathogenesis of the tumor is not certain, the most common theory relates to aberrant primitive mesenchyme development of the portal tract likely pertaining to the bile ducts. As rare as MHL is in children, there have only been 30 adult cases reported in the literature. Recent cytogenetic studies have shown that genetic rearrangements at chromosome 19q13.4 are linked to the development of hamartomatous tissue, as well as potentially linking MHL to malignant undifferentiated embryonal sarcoma (UES).Methods A 53-year-old white female was evaluated for a liver mass that was found incidentally during an evaluation for ureteral stones. Initial CT scan showed a cystic lesion in the right lobe of the liver and a laboratory evaluation was unremarkable. Follow up imaging revealed an increase in the size of the mass with changes in its characteristic - solid and cystic components. Percutaneous biopsy was nondiagnostic. In view of the recent change of the lesion and a nondiagnostic biopsy, the decision was made to extirpate the lesion. ResultsThe patient underwent a right trisegmentectomy and cholecystectomy. The pathological report was a 9cm x 9cm x 7.5cm, well-circumscribed, pink-yellow-tan, gelatinous mass, with a 1 cm clear surgical margin. The mass was cystic in the central portion and contained 30 mL of clear, yellowish fluid. Histologically, the mass consisted of rare benign dilated bile ducts corresponding to the cystic areas noted grossly, as well as myxoid stroma with spindle cells showing smooth muscle differentiation confirmed by positive staining for vimentin, smooth muscle actin and desmin. CD34 and hormone receptor studies were negative, thus excluding solitary fibrous tumor and angiomyxoma. The patient’s hospital course was uneventful and was discharged home on postoperative day five.ConclusionMHL of the liver in adults is a rare and potentially premalignant lesion that presents as a solid/cystic neoplasm. Symptoms are typically nonspecific, though abdominal pain predominates. Laboratory results are non-contributory and radiographic imaging is variable and inconclusive. Needle biopsy is rarely diagnostic and surgical excision of symptomatic or enlarging lesions is recommended to exclude the possibility of malignancy and establish a further diagnosis. The emerging literature supports a relationship between MHL and UES in regards to cytogenetic analysis, as well as histological similarities supporting a recommendation of aggressive surgical management when feasible.